Electric control system



Jan. l5, 1935.

A. J. SORENSEN ELECTRIC CONTROL SYSTEM Filed Nov. l, 1952 l 3 Sheets-Sheet l HIS A TTORNEY Jan.

A. J. SORENSEN ELECTRIC CONTROL SYSTEM Filed Nov. l, 1932 5 Sheets-Sheet 2 Z l gm l 50001101; L L9 -95 d" j' 122 125 m n E6 -1- W 25; Q7 A 126 7g) 114 11.5 50 i 82, l lfl 111 110 AM F1 "9g L1 lAmZLFL'eP 'lzfef 134 115 ign- G 85 86 152 -f 155 091101011501 l 1211 l21100 i Il? 150 M12 @Y j,

1| C01 l FV l C'ozzlzzep INVENTOR FW. Z. AndPewQ/.Sorelzsp/z BY @ECM/W192i@ HIS ATTORNEY ELECTRIC CONTROL SYSTEM Filed Nov. 1 1932 3 Sheets-Sheet 3 "L 58 3g V Generador MI 27 @7b/wf@ f 75 :Vm-76 A vi W A a 60A Cauzzer j vENroR' f'lg. 5. AndmwJ ransom BY. @RM

HIS ATTORNEY Patented Jan;V

lMy invention relates to electric control systems, l

and'particula'rly to electric control systems for railway trains. 1 j Y v j VIfwill describe'rcertain forms ofapparatus em-r .5"'bodying my invention, and will then point out the novel features-tlfiereof in claims. l y

In theaccompl nyingV drawings,L Figs. v1 and2 constitute a ldiagrammatic view showing one form .vofmapparatus embodying nflyinvention when apl plied to? a communicating and brake/control system for a railway train. Thev apparatus'of-Fgyl isfthat located at the control-point,y which in this instance, Yis ontheY locomotive, and this apparatus .(is'governed in accordance vwiththe position'of the lwusual engineers brake valve.V The apparatusof Fig. l2 is that'located atf another po-intgonthe` trainffor controlling an auxiliary brake controlling mechanism. Whilerthe apparatusof Eig. 2

may `her-located at anypoint onr the train',l it'willv zo be considered in the followingdescription as {bev ingV mounted inthe Ycabooseof a freight train. The apparatus of lFigs. l andy Zisalsoja'daptedto exchange code f messages Abetween the two --locations. Fig. 3 is a diagrammatic view ofa modified Y form of the apparatus at thecontrol pointwhich also embodies `my invention'.-

Y' Y v Although I am here disclosing a specific appli-r cation of my invention, it will be understood that I do not wish to limit myself to` control systems for railway trains only, as my inventionis equally useful for other control systemswherein mechanisms located at two remotely located stations are operatively associated with each otherrw e In control systems of the type here involved diierent control codes each consisting of a carrier frequency current modulated by a low frequency current are conveyed betweenntwo remote locations over a single communicating circuit. Fur-` thermore, in order to maintain an established f* condition at each location the code impulses `are alternately exchanged between the two locations over this single communicating circuit. A feature of my invention is the provision of new and4 improved apparatuswhereby an established condition at each of two remote stations is maintained by the exchange of code impulses only at spaced intervals. That is, the transmitting and a smallfractionof ithe time, amuch longer lifev for the'equipment is obtained; especially is this munication'between the two ends of a train iseac` ractersr designate `similar parts.,

trueffor the vacuum tubes commonly employedff by systems Vsuch as here'involvedrasV generators.;y of the carrier currentandof the modulation 'cur-'-; rent. y The inactive interval between two succesi -sive periods-of exchanging impulses` also insures jv- 5 that inthe operationof transferring-the equipa r; ment from ihe'conditionfor serwlinsxn.one-direcer r 4tion tothe condition forrsending, the opposite-;

direction, any ordinary delay inshiftingthe'appaf ratus fateither location does not `result in the i l0 shortening ofcne'of thev impulses .and asubsequent IQSS 0f Control-l Oihereatures of mmm-:1 i:

vention will-appearas the specification progresses. a The communicating circuit extending f rorn one;

,location tothe other, in this instance between'the5l IA U locomotive andthe'caboose of a freight train,v may takedifferent forms butV a preferredgform isjthatl, disclosed and claimed inthe L, O.-Grondahlapf plication Serial No. 450,135,Y-r filed'May 6. 193D j'fforrElectric -trainsignaling systems, wherein-com complished throughA the medium ofthe traiicg Tails-ii 5 i j i 1 In each of theseveral views like reference'char;

Y Referringl tojFigel, the referencacharacter.EV-i; j designates the usual engineersbrake valve ofthe Standard' typefihavine the usualrelease; running, v lanserve .and emeleeny positonsfor eStablish-- r ying the cor-resp*endingabrakeA conditionsaof the 30 f tact segments?! ands, respectivelyfinboth the-'354 service and emergency-positions of handle 3.3 The contaetor Gris adapted toengage a-icontactv seg-.j` ment 9 Vinhetll the releasea'nd :running positionsifn and cQliaffeem-Qnt; 110., :llf'and 12 infthelap;

service andfjemergency positions;jrespectively. Y'4.0

The function of this vcontact assemblyjassociated.V with the brake'Valve-EVwill appear as -the specifi-fyi cation progresses. 5 L

The locomotive is equippedwith a generator'G of carrier;frequency/'current and threegeneratorsg45 u Venient frequency; adaptablefor such' systemes,=j50

I shall refervin-the followingdescriptionftozithef q frequency of generator G as being 5000 cycles per" j ksecond and the. frequencyl ofthe imoc'iulators"v M1',

second, respectively. It Will be understood, hoW- 55 ever, that my invention is not limited to these specific frequencies but they are given by way of illustration only. The generator G and the modulators M1, M2 and M3 may take any one of several well known forms for such devices among them being the vacuum tube type, and as the specific type of these generators forms no part of my invention, they are shown conventionally only, in order to simplify the drawings as much as possible.

Modulator M2 is adapted to modulate the carrier frequency current in the release, runningr and emergency positions of the brake valve EV, To be explicit, with the handle 3 in 'either the release or running position, a circuit can be traced from the upper terminal ofmodulator M2 along wire 13, back contact of the armature 14 of a relay 15 to be referred to later, wire 16, con-v tact segment 9, contactor 6, vwire '17, vgenerator G and wire 18 to the opposite and lower terminal of modulator M2. When the handle 3 is movedaround'to the emergency position, the circuit extends' from the upper terminal of modulator M2 over wires 13 and 19, contact segment 12,' contacter 6, and thence as before traced throughthe generator G and to the lower terminal of modulator M2. The modulator M1 is active to modulate the 'carrier frequency current under the lap and service positions ofthe brake valve EV; With the handle 3 in the lap position a circuit can be traced from the upper terminal of modulater M1 along wire 20, backv contact of the' armature 21 of relay 15, wire 22, contact segment 10,' contactor 6, wire 17, generator G, and wi`re`18 to the 'opposite and lower terminal of modulator' M1.' When the handle 3 is moved to the service position,` the circuit for modulator M1 extends fromfi'ts upper terminal along wires 20 and 23,`contact segment 11, contactor 6, and thence as before traced. At such time as the relay 15 is energized in a manner to later appear,

and its armatures 14 and 21 are raised'into engag'ement 'with their respective front contacts, the modulator M3 is rendered active to modulate the carrier frequency current if atthe same time,

- the brake valve handle Soccupies either the release, running 'or 1315 positio'nyas will be readily understood by an inspection of Fig. l1. It follows that the modulator AM2 is rendered active to modulate the carrier frequency current in the l-release, running and emergency positions of handle'3; the modulator'Ml is rendered active in the lap and service positions, and the lmodulator M3 is activein the eventthe relay 15 is energized at a time ywhen the -brake valve handle 3 is in 'either the release, running or lap position.

24'and 25 are induotor'coilsV mounted on the locomotive in inductive relation with the traffic rails' 1 and l, respectively. vBy means of these inductor coils the carrier frequency current from the'generator Gis supplied'to the traffic rails and' to this'end they are at times included in a transmitting circuit'that also includes the output of the generator G. This transmitting circuit extends from' the upper right-hand terminal of z`i,'enerator G'along wire 30, coilsY 25 and 24 in series, wire 29, the' front contact of armature 27 of a"rela`y 28 tov be referred to` later, and thence by wire 26tothe opposite and lower right-hand terminal ofl generator 'GQ Consequently, at such 'periods' 'as' the .relay 28 is piclfred up, modulated carriencurrent is deliveredA to the traincV rails landl.

The' locomotive apparatus includes a mechanically tuned oscillato'r Nil This 'oscillator' may take any one of many forms such, for example, as that described in the United States Letters Patent No. 1,858,876, granted May 7, 1932, to P. N. Bossart, for Coding apparatus. It will, therefore, suffice for this description to say that between the pole pieces P1 and P2 of a field structure J there is mounted an armature H pivoted at O. The armature H is biased to a mid-position Where the contact members 31 and 32 operated by armature H, occupy the position indicated by the heavy lines in Fig. 1. A field winding,33 is connected to a source of current, such as a battery 34, by a simple circuit that includes the contact member 31. The energizing of the eld winding 33 causes,the armature H to rotate in a Vclockwise direction as indicated by an arrow.

is thus energized. The biasing force and the Weight of armature H are made such that it will have a natural period of oscillation of say,

60 cycles per minute, although it' will be understood another frequency may be selected if found desirable. During the interval armature HV is rotated in the clockwise direction v due to the energization of eld'winding 33, the contact member 32 is -swung to the'left to engage a left-hand contact 36, and during the reverse movement of armature H the contact member 32 is swung to the right to engage a right-hand contact'v 37. Hence," the contact member 32 is continuously oscillated between the two contacts 36 and 37 at the rate of 60 times per minute making engagement with each contact once 'each second. As will shortly appearjtwoY complete swings of contact member 32 constitute anv operating cycle, which cycle is divided into four periods of approximately one-half second each. v

Three relays 38, 39 and 28 are associated with the oscillator N in the following manner. Sup- ,l

pose that all ythree relays 38, 39 and128v are de-` energized and the Contact member` 82 is first swung to the left to engage the contact 36. During the period the contactmember'32 engages the left-hand contact 36 which period forms the first one-halfv second period of the operating cycle, current flows from the positive terminal of battery 34`ov'er wire 40,'back contactvof the armature 41 of relay 39, top win .dingfofA relay 33, left-hand contact`36, contact member 32 and thence to the negative terminal of"ba'ttery 34',4

and relay 33 lis piclrefd" up. When. the contact member 32 changes positions to make engagement with the right-hand contactv 37 to start the n second one-half second period of thev operating cycle, the relay 38 does l notdrop because is slightly slow-releasing yin character. Y A circuit can now be'traced from the positive 'terminali of battery 34 along wires 40Y and 42, frontcon'ta'ct of the armature 43 of relay 38,'lower winding of Vrelay 39, contact 37, contact member 32 and to the negative terminal of battery 34, and relay 39 is picked up. Another circuit branches from the wire 42 through frontr'contavct of the armature 44. of relay 38, lower winding of relay 38,

winding of relay 28, wire 50, contact segment 7,

wire 45', contact 37 and contact member 32 to the negative terminal of battery 34, and relay 38 is given an energizing impulse. Thus both relays 38 and 39 receive an energizing impulse during the second one-half second period in the operating cycle of the contact member 32. When the contact member 32 next swings to the left to again engage contact 36, that is, during the third one-half second period of the operating cycle, the relay 39 remains picked up as well as relay 33 due to relay 39 also being slightly slow-releasing in character. Hence, while contact member 32 engages contact 36l during this third one-half second period of the operating cycle, the first traced circuit to the upper winding cf relay 38 .is held open at the back Contact of armature 4l and relay 38 does not receive an energizing impulse. Current does now flow, however, frorn positive terminal of battery 34 over wire 40, front contact of armature 46, top winding of relay 39, Contact 36 and contact member 32 to the negative terminal of battery 34 and hence relay 39 is given an energizing impulse during this third one-half second period. The release period of relay 38 is made such that before the contact member 32 next swings to the right to engage the contact 37 and thereby close the circuit to the lower winding of relay 33, relay 38 drops. Thus, during the fourth one-half second period of the operating cycle in which the contact member 32 engages the contact 37, the circuits to the lower winding of both relays 39 and 38 are open at the front contacts of armatures 43 and 44, respectively, and neither relay 38 nor relay 39 receives an energizing impulse. The release period of relay 39 is made such that before the contact member 32 next swings to the left, relay 39 releases, and thus both relays 38 and 39 are down ready to start the operating cycle all over again as the contact member 32 makes its third successive swing to the left to engage the left-hand contact 36. It will be seen from the above that for each two second interval required for the contact member 32 to make two complete swings, the relay 39 is picked up during the second and third one-half second periods and is down during the first and fourth one-half second periods.

During the third one-half second period ofthe operating cycle, while contact member 32 is swung to the left and relay 39 is picked up, current flows from the positive terminal of battery 34 over wires 40 and 47, winding of relay 28,`

is picked up. Relay 28 immediately drops when the contact member 32 next swings away from the contact 36 and hence relay 28 is picked up once each operating cycle, that is, it is picked up during the third onehalf second period of each two secondinterval. As pointed out hereinbe.- tore, when relay 28 is picked up to close the fro-nt contact of its armature 27, the transmitting cire cuit is closed and the traffic rails are supplied with an impulse of carrier current modulated in accordancewith the position of the brake valve EV, That is t say, the apparatus of 1 supplies an impulse of modulated carrier current to the communicating circuit during the third one-half second period of each two second inter.- val. It is to be noted. that when the valve handie 3 is moved to either the service or emergency position, the relay 28 is held steadily energized `by current from battery 34 over wires y4() and47,

contactor 4 and thencefby wire 51 to the negative terminal of battery 34. It is clear, there fore, that under the service and emergency positions of the brake valve EV the locomotive apparatus continuously supplies modulated carrier current to the traffic rails.

During such time as the relay 28 is deenergized and its armature 27 engages its back contact, the inductor coils 24 and 25 are connected to a receiving circuit for receiving energy picked up from the traic rails. This receiving circuit extends from the upper left-hand terminal of an input iilter F1 over back contact of armature 27, wire 29, coils 24 and 25 in series, and wires 30 and 52 to the upper right-hand terminal of iilter Fl. kThe lter F1 is preferably a band pass filter adapted to select frequencies of a modulated carrier current supplied by the caboose apparatus to be described later. The current selected by the :Filter F1 is passed over the wires 53 and 54 to the input of an amplifying device AM which is adapted to amplify and detect the modulated carrier current and cause to appear in its output circuit variations corresponding to the modulation frequency only. The filter F1 and amplifier AM may take any one of several forms well known for such devices and as their specific structure forms no part of my invention, they are shown conventionally only.

The output of amplifier AM is supplied to the sharply tuned circuit networks 55 and 56 which are tuned to respond to the frequencies of the modulators M2 and M1 of the caboose apparatus, respectively. The network 55 includes a condenser 57 and a reactor 58 in series, a portion of reactor 58 being connected to the input of a full wave rectier 59, the output of which is connected to the winding of a relay 60. In like manner, the network 56 includes a condenser 61 and a reactor 62 in series, a portion of reactc-r 62 being connected to the input terminals of a 'ullwave rectifier 63, the output terminals of which are connected to the winding of a relay 64, Consequently, whenever carrier current modulated at the frequency of modulator M2 is picked up from the traffic rails, the relay 6i) is energized, and if the modulation is of the frequency of modulator M1, the relay 64 is energized. Relays 60 and 64 control over front contacts a simple circuit for the magnet 65 of an electropneumatic valve DEZ, and the indication lamp 66, the circuit being such that when either relay is energized, magnet 65 is energized and lamp 66 illuminated as will be readily understood from an inspection of Fig. 1. i

The valve DE2 is biased to the open position and is held closed by the energizing of the magnet 65. When the valve DEZ is open, the train brake pipe designated by the reference character BP is connected to the atmosphere through a vent of such characteristics as to cause an emergency application of the train brakes. It will be understood, of course, that valve DEZ may be arranged to provide a lighter brake application should it seem desirable to do so. It is to be noted that whenever the valve handle 3 is moved to either the service or emergency position, the magnet 65 and the indication lamp 66 are supplied with current by a circuit that includes the contact seg- 7 ment 8 and contactor 5 of the contact assembly.

Whenever the relay is picked up, current is also supplied to a signal bell 68 and to a counter device indicated by the reference character CG, by a simple circuit easilytraced, whichincludes ceiveclfromV the traflc rails by the cabo-ose Itangular symbol only for the sake of simplicity.

Thefunction of the signal bell 68 and of the counter CO will appear when the operation of theY apparatus is described.

Depressing a signaling key K to bring a con- 'tact 69 into the position indicated by dotted lines in Fig. 1 causes current to be supplied to the relay 15 from `the positive terminal of the current source over contact 69, winding of relay 15, transfer contact element 70, back contact ele- /ment 71, wire '72, back contact of armature 'Z3 of relay 28 and to the negative terminal of the current source to pick up relay 15. Once picked up, relayV 15 will be retained energized by a stick circuit extending from the positive terminal of the current so-urce up to its winding as before traced and thence through the transfer contact elementfl, front contact element 7d and to the negativeterminal of the current source. Thus, although relay l5 can be picked up only during the interval the relay 28 is deenergized, once picked-up .itwillbe retained energized as long the signaling key K is depressed. As previously pointed out, thepicking up of relay 15 causes the modulatorM3 to become active in place of either modulator M1 kor M2 in the event the brake valve EV occupies either the release, runningor lap position. t is to be noted that relay l5 .also controls a .circuit for the signal bell 68 andcounterCO. which extends from the positive terminal of the battery through bell 68 and Winding of counter CO. inv parallel front contact of armature 'l5 of relay 28 and front cont ct of armature 76 of relay l5 to the negative terminal of-the battery.

Referring to Fig. 2, inductor coils *.end 7S aremountedat thecaboose in inductive relation with the traic'rails .l anilla in a manner similar-.to the coils 24 and 25 on the locornotie. means of .coils 77 and 78 energy is at time paratus,.whilefat other Atimes energy is tothe traffic rails by the Caboose When energy is picked up from the tra by coils ,'77 dhd78, it is applied to an input filter Frover areceiving circuit extending troni the upper right-hand terminal of filter F1 through wire 82, back Contact of the armature of a relay'lto be reierredgto later, wire T9, coils 77 and '78 and wire SSto the lower right-hand terminal of `lter F1. It will be noted that this receivingcircuit is also closed at the front contact of armature 1l0 ofr a relay 92, whenever ti relay is energized. Filter F1 is a bandpass flits," preferably similarrto the iilter F1 of 1 and this filter on the cabcose is vadapted to pass trequencies of the range of Vthegenerator G on the locomotive when modulated at the frcquenc of .pany loneof the locomotive modulators L1, I or'M3. Energy passed by the lter Fl is appli to the input of an amplifying device AM similar totheainplyfying'device of 1. r`his cabe-cse amplifienAM amplies and detects the current received through the filter F1 and causes to appear: in its'output circuit variations corree 'spondlngltothe `modulation frequency only; The

variationsof the output of amplifier AM-are applied to the sharply tuned circuit networks 84, and 86 which are responsive to the modulation frequency of modulators M1, M2 and M3, respectively. Relays 87, 88 and 89 are controlled by the circuit networks 84, 85 and 86, respectively, and thus it follows that relay 87 will be picked up in response to the modulation frequency of modulator M1, relay 88 will be picked up in response to the modulation frequency of modulator M2 and relay 89 will be picked up when the modulotionl frequency is that corresponding to the frequency of modulator M3.

The energizing of relay 87 causes current to flow from the positive terminal of a source of current such as a battery 90 over Wire 91, winding of relay 92, top winding of a polar relay 93, wire 94, front contact of armature and thence to the negative terminal of battery 90. Relay 92 is a neutral` relay and will be picked up in the usual manner in response to the energizing of its winding, and relay 93 is a polar relay so arranged that the energizing of itstop winding by current flowing in the circuit just traced will cause its polar armature 96' to be held in the left-hand position, that is, in the position opposite to that shown in Fig. 2. The picking up of relay 88 causes current to flow from the positive terminal of battery 90 over wire 91, winding of relay 92, lower winding of relay 93, wire 97, and front contact of armature 98 of relay 88 to the negative terminal of battery 90. Relay 92 will be picked up the same as before but the polar relay 93 is so arranged that the energizing of its lower winding by current flowing in this lastcircuit will cause its polar armature 9S to be held in the right-hand position, that is, in the position as shown in Fig. 2, Relay 93 is also of the type that its polar armature is retained firmly in the position to which it was last moved during such time as the winding of the relay is deenergized. The picking up of relay 89 causes current to flow from the battery 90' over wire 91, winding of relay 92, wire 99, winding of a neutral relay 100 and thence over the front contact of armature 101 of relay 89 to the negative terminal of the battery 90. t follows that current modulated at the frequency of modulator Ml causes relay 92 tol be picked up and the polar armature 96 of relay 93 to be held in the left-hand position. If the modulation is that of modulator M2, the relay 92 is picked up as before and the polar armattu'e 96 is held in the right-hand position, while if the modulation frequency is that of modulator M3, the relays 92 and 100 are energized in series.

As indicated in Fig. 2, the relay 81 is slowreleasing in character and is adjusted with a release period of from one-fourth to one-half second, relay 194 is slow-releasing in character and adjusted with a release period of one-half to one second, and relay 103 is slow-releasing in character and adjusted with a release period of at least two seconds. Relays 81, 103 and 104 are governed by the relay 92 in the following manner. As long as relay 92 is deenergized, relay 10a is picked up by current from the battery 99 over a simple circuit that includes-the back contact of armature 102. Whenever relay 92 is energized, relays 103 and 81 are energized in parallel by a circuit that includes the front contact of armature 102. As will shortly appear, this group of relays governs Vthe operation or" an auxiliary brake controlling. mechanism mounted through a vent of such characteristics as to propolar armature 96 and to the negative terminal in the caboose, and also' the sending of indication impulses.

The auxiliary brake controlling mechanism'in lthe caboose comprises a main reservoir MR, a feed valve FV and electropneumatic valves DR,

DS, DE and DEl. The caboose,'of course, will also be equipped withv a compressor, air gages and all other equipment necessary to insure ample supply of air pressure in the main reservoir MR independent of the usual supply of air pressure on the locomotive'. Valves DR, DS and DE arev each biased to the closed position and are lifted to the open position whenever the magnets 105, 106 and 107, respectively, are energized. The valve DEl is biased to the open position and is heldclosed by the energizing of its magnet 108. Whenever the valve DR is open and the remaining valves are closed, the train brake pipe BP is supplied with air pressure through the feed valve FV and the auxiliary brake controllingV mechanism reproduces the running condition of the engineers brake `valve f EV onv the locomotive. With the valve DS open,

the brake pipe BP is connected to the atmosphere through a vent of such characteristics as to produce a reduction of brake pipe pressure at substantially the service rate and, consequently, a service application of the train brakes.

When either the valve DE or DEl is open, the brake pipe is connected to the atmosphere duce the emergency rate of reduction in the pressure of the brake pipe and an emergency application of the train brakes. It is to be noted that valve DE is biased to the closed position and opened in response to the energizing of its magnet 107, while the valve DEl is biased to the open positionand is held closed by the energizing of its magnet 108.v That is to say, there is provided one valve that establishes an emergency brake application in response to an impulse of control current and a second valve that is active to establish an emergency brake application When all control current fails. When all four of these valves are held closed at the same time, both the supply and the exhaust for the brake pipe BP are blanked and the auxiliary brake mechanism in the caboose reproduces 'the lap condition of the engineers brake valve EV.

At such time as relays 103 and 104 are. both lpicked up and the polar armature 96 of relay front contacts of armatures 118 and 119 of relays 103 and 104, respectively, right-hand contact of polar armature 96 and to the negative terminal of battery 90. The opening of valve DR in response to this energizing of magnet 105 closes a contact 120 whereby current then flows to the winding of magnet 108 by a simple circuit easily traced. Magnet 108 is also energized at times by current flowing in the circuit from positive terminal of battery 90 through winding of magnetl 108, Wire 121, front contacts of armatures 122 and 123 and thence through the lefthand contact of `armature 96 to the negative terminal of battery 90. At such time as relay 104 is down, relay 92 is picked up, and polar armature 96 is in the left-hand position, so that the magnet 106 of valve DS is supplied with current from positive terminal of battery 90, Winding of magnet 106, back contact of armature 124, front contact of armature 125, left-hand contact of of battery 90. In case polar karmature 96 is toward the right at a time when relay 104 is down and relay 92 is picked up, the magnet 107 of valve DE is supplied with current from positive terminal of battery 90 through winding of magnet 107, back contact of armature 126, front contact of armature 127 and thence through the right-hand contact of polar armature 96 to the negative terminal of battery 90. n

As previously stated current is at times supplied by the caboose apparatus to the traic rails l and la, and to this end the apparatus of Fig. 2 includes a generator G of carrier frequency current and two modulators M1 and M2 all preferably similar to the corresponding devices of Fig. l.v The transmitting circuit wherewith the generator 'G is effective to supply current to the coils 77 and 78 extends from the upper right-hand terminal of'gen'erator G throughwires 109 and 83, coils 78 and 77, wire 79, back contact of armature 110 of relay 92, front contact of armature v111 of relay 81 and to the upper left-hand ter- Y minal of generator G. Normally, the modulator M1 is active to modulate the carrier current by a circuit controlled by relays 103 and 104. To be explicit, this circuit includes upper terminal of modulator M1, back contact of armature112of a relay 113 to be later referred to, front contacts of armatures 114 and 115, generator G and wire 116 to the opposite terminal of modulator M1. At such timeas relay 113 is picked up this modulating circuit is transferred from modulator M1 to the modulator M2 by the raising of the armature 112 into engagement with its front contact.

In describing the operation of the apparatus of Figs. 1 and 2, I shall assume the oscillator `N to be in operation for operating the relays 38, 39 and 28 in the manner hereinbefore described. I shall further assume that the engineers brake valve EV is rst set in the running position Where modulator M2 is made active to modulate the carrier current supplied by the locomotive Agenerator G. Recalling that the relay 28 is picked up during the third one-half second period of each two second interval, it follows that during this third one-half second interval an impulse of carrier current modulated in accordance with modulator M2 is supplied to the traiiic rails, while for the remaining three one-half second periods of each two second interval the relay 28 is down and the locomotive apparatus is in the receiving condition.

At the caboose the receiving circuit is normally closed at ythe back contact of armature 80 and hence the impulse now transmitted from the locomotive is picked up and applied through the filter Fl to the input of the amplifying device AM and the relay 88 is energized. At the end'of the impulse relay 88 will immediately drop. In response to this operation of relay 88 the relay 92 is picked up and the polar relay 93 operated to its right-hand position, the-relay 92 becoming deenergized immediately after the deenergizing of relay 88 while the polar armature 96 of relay 93 will remain held in the right-hand position. It follows that relay 92 will be operated the third one-half second period of each two second interval, or in other words, will be picked up during one onehalf second period, and will be down the remaining three one-half second periods of each two second interval. Relay 104 being energized when'relay 92 is down and being provided with a one-half to one second release period, it will not release during the one-half second period that relay 92 is picked up.' Relays 81 and 103 are en- Y ergized with relay 92 picked up and as relay 103 is provided With a two 'second release period, :that relay will not release during the three onefhal.F second periods that relay 92 is down, but i as the release period of relay 81 is of only onefourth to onehalf second duration, that relay will release during each period that relay 92 is deenergized. Relays 103 and 104 are thus both` picked up and the polar 'armature 96 is held in the right-hand position in response to the impulses ncW transmitted from the locomotive. The magnet 105 of valve'Dl-t is thus energized to `close the valveDR and to complete the circuit for the magnet 108 of valve DEl. With valves DS and DE biased to the closed position and with `valve DR now held open by the magnet 105 and ferred to the transmitting circuit and the traic rails areA supplied with a return impulse of carrier frequency current modulated at the frequency of the Caboose modulator M1. On the locomotive the releasing of relay 28 to terminate the sending of a control impulse closes the receiving circuit on the locomotive and thus the return impulse transmitted bythe caboose apparatus is picked up by the inductor coils Z4 and 25 and applied to the amplifying device AM to energize relay 64. 4.The picking up ofv relay 64 in vturn causes current to be supplied to the magnet 65 of valve DE2 and to the indication lamp 66 with the result that'the valve DEZ is held closed and the lamp 66 displayed to indicate to the locomotive operator that the Caboose appa ratus has responded to the control impulses transmitted from the locomotive.

As long as the brake valve handle 3 remains in the running position, control .impulses will be transmitted therefrom the third one-half second period'of'each two second interval and the caboose relays 103 and 104 are held energized to establish the running condition of the auxiliary brake controlling mechanism. During a portion .of the one-half second period immediately following a control impulse thev Caboose apparatus is transferred to the transmitting condition and a return indication impulse supplied to the traiic railswhich is received at the locomotive and the relay 64 energized. Relay 64 being slow-releasing in character, it Will remain picked up from 4one return impulse to the next, so that magnet 65Will be steadily energized and indication lamp 66 continuously displayed. It is to be noted that in this operation of the apparatus there always -existstwo one-half second periods between the termination of the return indication impulse and theinitiating of the next control impulse, the relay 103 in the Caboose and the relay 64 on the locomotive being provided with a .slow release yperiod suiicient to span this inactive interval.

In the eventfthebrake valve EV is .moved to its lap position-the .operation of the apparatus on the locomotive is the same asdescribed for the lrunning position except for the fact that the control impulses are-modulated at the frequency .the train brakes. .andthe opening of valve `DE closes a contact of modulator M1 instead of at. the frequency of modulator M2. At the Caboose the relay 87--Will now be selected in` place of relay 88- and-thefpolar relay 98 shifted to the left-hand position. With. relays 103 and 104 picked up in response tothe operation of relay 92 and the polar armature 96 toward the left, the circuit to the magnet 105 is'open and valve DR Closes, and contact 120 in the circuit to Y.magnet 108 is opened, but magnet 108 will now be energizedby the circuit that includes the front vcontacts 122 and 123 and the left-handcontact of polar armaturel 96. Hence, .ie auxiliary brake controlling'mechanismnou1 reproduces the lap condition established by the brake valve EV on the locomotive. The return indication impulses' transmitted from vthe caboose remain the `same as under the running condition with the result that on the locomotive `the valve DEZ is held closed'and the indication lamp 66 displayed. Again, it is to be noted `that there exist two one-half second periods `between the termination of the return lindica- Vtion impulse andthe initiating ofthe next control limpulse.

In the event the brake valve EV ismoved to the service position, the relay 28 is held'energized irrespective of the operation of the'oscillator N and carrier current modulated at the frequency of modulator M1 is continuously supplied to the traic rails. ceipt of a prolonged impulse of: carrier current modulated at the frequency of modulatorl M1 causes relays 87 and 92 to be held energizedand the polar relay 93 to-be held in its left-hand position. The circuit tolmagnet 105 is now open O and valve DR closes atlonce. At the-end of the release period of relay 104, that relay drops to -completethe circuit to the magnet 106fand valve DS is opened toestablish a service application of the train brakes. As no'return indication impulses yareV now transmitted vfrom the caboose,

vthe relay'64 `on .the locomotive'releases at the `end of its release period'but magnet 65 of valve DEZ and lamp 66inovv receive current by the circuit that yincludes the contactor 5 of the Contact assembly. `The energizing of magnet 106 and the opening of valve DS on the Caboose closes a contact 128 to complete a circuit for the magnet 108 and'hence the valve DEI is retained closed, the magnet 108 being slightly slow-releasing in character to vhold the valveY closed during the'period of changing-from one brake condition to the other.

In the event the brake valve EV is moved to the emergency position the relay 28 is retained energized and a prolonged impulse is transmitted fromthe locomotive which is modulated in accordance with the frequency of modulator M2. At the caboose this prolonged impulse retains the relays 88 and 92 picked up and shiftsthe polar relay 93 to its right-hand position. At the end of the release period for relay 104, that relay releases and the circuit to the magnet 107 is completed andthe emergency valve DE is opened With the result that the-auxiliary mechanism establishes an emergency application of The energizing of magnet 107 129 so that the magnet 108 of the second vemergencyvalve DEl is still supplied with current. Gn the locomotive the Amagnet 65 and the lamp 66 receive current through the contactor 5 the same as in the service position.

. In the event a brake application is initiated at the valve DEZ as a result of a loss of return At the caboose the revindication impulses, the locomotive operator is able to at once take charge ofthe brake application by moving the brake valve handle 3 to either the service' or emergency position where the magnet 65 of valve DEZ is reenergized by th circuit that. includes the contacterV 5. Y It is to be observed that a change in the position ofthe brake valve EV from that of a running positionto that of a brake applying position immediately produces a corresponding change in the control impulses, the change taking place in step with the movement of the handle 3 irrespective ofthe point in the operating cycle of relays 38,139 and 28 at which handle .3 ismoved. At the caboose, a .change in the control impulse from that corresponding to a running position of4 the valve EV to that correspendingv to .a brake applying position, results inthe immediateresponse of relays 92 and 93. Magnet. 105 of valve DR, being non-slow-acting, responds assoon as its circuit is opened lwith the result that valve DR is at once closed to cancel the running condition of theauxiliary brake controlling mechanism.. The energizing oi magnet 106 or 107 to establish a brake applying condition will be delayed only to the extent of the slow releaseperiod of relay 104 inasmuch as one of the circuits for Vthese magnets will be completed as soon as relay 104 releases.y It will be recalled that relay 1041s without energizing current only during. the period a controlimpulse is received at the caboose which, under a running condition, occurs yonly during one one-half second period out of every two second interval; In other Words, therelease period of relay 104' need be but slightlygreater than one-half second in duration. With such an arrangement of apparatus it is apparent that a brake applying condition of the auxiliary mechanism inthecaboose Will be initiated substantially. one-half second after a brake applying condition has been established for the valve EV. l. have found that with apparatus such as herein disclosed the respense oi the auxiliarybrake Amechanism at the rear .of the train to a brake application initiated on the locomotive .will take place inless than one second. The advantage oi brake equipment at the rear of a train which .will respond to a'brake application initiated on the locomotive -in one second or less, will be apparent lto all familiar with the control of trains.`

To transmit a signaling message from the locomotiveduring the release; running orv lap position of valve EV, the operator will .depress the signaling key K to bring about the energizing oi` relay 15. The picking up or relay i5 will result, however, only at such time as relay. 23 is deenergized. Hence, although' signaling key K can be operated at any time relay. l5 cannot be pickedup except with the locomotive apparatus in the receiving condition thus avoiding the pos'- sibility of splitting a control impulse. Once relay 15 is picked up it remains so until the signaling key'K. is restored due to the stick circuit over the front. contact element '74, When relay 15 picks .upythe transmitted impulse will be modulated at Vthe frequency of modulator M3 in place of being modulated byv either M1 or M2 with the result that the relay 39 at the Caboose Vwill be operated. Operating relay causes in turn operation of relays` 92'and 10G, leaving the polar relay 93 in the position it occupied before signaling was initiated. Operation of relay 92 controls the relays 103, 104 and 31 .the sameV as before,

' l so that the condition tof. the auxiliarybrake controlling mechanism .remains unmolested, .during the sending of a signal message. With relay 100 operated, current is supplied by a simple. circuit easily traced to a signal bell 130 and to a counter device, designatedk by the reference character CO1 andpreierably similar to counter CO on the locomotive. While relay 100 .may be slightly slow-releasing its release .period should be short enough to allow `the relay to dropv between two successive impulses. Hence .the signal bell .130 andthe counter CO1 will receive an energizing impulse lor each impulse picked up from the Atrahie rails. On the locomotive operationxof the key K and `subsequent picking up of relay. 15 results in the signal bell 68 and counter CO receiving an energizing impulse during each period oi transmitting an impulse to the trailic. rails due to the. circuit for bell 68 and counter CO being controlled at the front contact of armature 'Z5 oi relay 28 andthe front contact of armature 76 of relay 15.

` The locomotive operator will, thereforehold key K depressed and count the number of transmitted impulses by listening to the bell .68. and by observing the numeral displayed on the counter COuntil Vthe number of impulses .sentout correspondto the prearranged code message he desires to send. At the Caboose the operator will likewise count the signaling impulses by listening to the bell 130 and by observing the numeral displayed on the counter CO1. At the endof the code message the locomotive operator restores the key K thereby stopping the sending of signaling impulses due to relay 15 becoming at once deenergized. .The caboose operator can check the code message as he will have a permanent record of the number of impulses registered by the `counter CO1; Both operators vwill now manually restore the respective counters to their starting point as is customary for such` devices; As soon as relay 15 releases, the control impulses are resumed and the condition existing before signaling was initiated is restored. It is to be observed that thecaboose apparatus'continues to transmit indication impulses during the time of signaling and thus on the locomotive the magnet 65 and the lamp 66 are not molested.

To signalfrom the Caboose the Caboose operator will Adepress the signaling key K1 to bring rthe contact 131 to the position indicated byA dotted lines and therebyclose a circuit for the relay 113, whichcircuit extends from the positive terminal of' thesource of current through contact 131, winding of relay 113, transfer element. 132, baclecontact element 133, back contact of armature 134 of relay81 and thence to the negative terminal of the current source. Although key K1 caribe operated at any time it is clearthat relay 113 can bepicked up only during the receiving period for the Caboose apparatus thus avoiding the possibilityy of .splitting a return indication impulse. Relay 113 kwhen once picked up remains energized by a stick circuit that includes the front contact 135, until such time 'as key K1 is restored. With relay 113 picked up the rreturn indication impulses are modulated at thefreduency'of modulator M2 in place of at the frequency oi modulator. M1 and thus the relay 60 on the locomotive responds to the return impulses.v With relayY 60 picked up, the circuit tothemagnet`65 and lamp @Gis still completed. Relay' may be slightly slow releasing in character but its releaseperiod should be made somewhat less .than Ythe interval'between two return impulses so that .it releases. for .each impulse vre ceived. `Itisito be'observed'ithatmagnet 65 is slow-releasing in character and will thus hold valve. DE2 closed during the period that. relay l60:.is down. Each time relay 60 is picked up,

the signal bell 68 and the counter CO receive an energizing impulse. On the caboose, after the key K1 .has been operated and relay 113 picked up, the signal bell 130 and counter CO1 will be energized during each sending period due to a circuit that includes the front contact of armature 136 of relay 113. and the front contact of armature 137 of relay 81. The caboose operator will thus hold key K1 down and count the impulses transmitted .by listening to the bell 130 and by observing the numeral displayed by counter CO1 until the number of transmitted impulses correspond to the code message he desires to send, at which .time he will restore key K1 causing the relay 113 to release and restore the modulator M1 to itsactive condition. On the locomotive the operator will now count the signaling impulses received by listening to thebell 68. and by observing the numeral displayed by counter CO. At the completion of the code impulse the locomotive operator will check the number registered on counter CO and then manually restore the device CO to its starting position.

It.follows, that to signal from either location tothe other the operator at the sending location holds closed a signaling key, the apparatus then functioning to automatically transmit the impulses of the code message, making both a visual and an audible register of the number of impulses transmitted. When the number of impulses correspond to the desired code message, the signal key is released and the apparatus is restored to the original operating condition. The .signal impulses not only acuate the signaling apparatus but also maintain the original condition of the operating mechanism during the signaling period.

With the oscillator N operating at the speed of 60 cycles per minute, that is, one cycle per second, the code message impulses will be sent at the rate of one every two seconds the same as the control impulses. In Fig. 3, there is disclosed a modified fonn of apparatus for the locomotive Wherewith the code speed is doubled when messages are to be transmitted either fromk the locomotive or from the caboose, thus completing a message in half the time required by the apparatus of Fig. 1. The apparatus of Fig. 3 is similar in all respects to the apparatus ofA Fig. l except that two relays 60A and 138 are substituted for relay 60 of AFig. l. Relay 60A is non-slow-acting and is controlled directly by the circuit network the same as relay and thus relay 60A'responds to the modulation frequency of modulator M2 and will be operated directly in step with the impulses energizing the network`55. Relay 60A controls through the front Contact of its armature 139 the relay 138, as Well as the signal bell 68 and counter CO. While relay 60A, signal bell 68 and counter CO will operate in step with the code message impulses, the relay 138 will be retained picked up throughout the entire signaling period, due to its being slow-releasing in character. Relay 138, bell 68 and counter CO will also receive an energizing impulse during the transmitting of the signaling impulses from the locomotive as well as when the relay 60A is being operated by the received signaling impulses, due to the fact that they are, also. controlled over the front contact Y of-armature '75.of'relay 28 and thefront contact igeemus of'armature 76\ofrelayf15. It will thus be seen thatlrelayA 138 isretainedpicked up whenever code messagesare sent either from the locomotive or from the caboose. Relay 138 controls at the front contact of its armature 140a shunt path extending around the front contact of armature 48 of .relay 39. It will be recalled that armature 48 of .relay 39, in conjunction with the left-hand contact 36 `of contact member 32, controls the operation of` relay 28 under the release, running and lap positions, thecontrolbeing such that one operation of relay 28 corresponds to two complete swings of the contact member 32. That is, relay 28 is picked up only vduring one one-half second periodout of each-two second interval. With relay 138 picked up, therelay 28 will be energized each time the contact member `32.swings to the left and thus relay 28'will now beoperated once foreach swing ofv contact member. 32 which is double the ratewhen relay 28 is also controlled .by relay 39.y As relay 28 governs vthe transferring received at the Caboose has terminated, it is clear that the rate of sendingthe codeinessage impulses is twice the. normal rate when sent from the caboose'as Well as when sent from thelocomotive.

It is apparent from the foregoing, that the opy eration of `my system, when the control location is provided with .the apparatus of Fig. 3, will be similar to that already described for Figs. 1 and 2, except for the fact that vwith the apparatus of Fig.- 3 the sending rate ofthe code message impulses will be twice the normal rate of the control impulses.

A control system such as here disclosed requires the generators of the control current, which ordinarily involves the use of vacuum tubes, to be active onlyduring a small portion of the time thereby insuring a long life for such devices. By providing an inactive interval between each exchange of "impulses the overlapping of a return impulse with the next control impulse is avoided and a more reliable operation obtained. The code message impulses are automatically transmitted in response tothe operator holding his signalling key closed until the. proper number of impulses have been registered at each location thereby insuring greater accuracy in both the sending and the receiving of the code messages. Furthermore, in order to facilitate the rapid sending of the code messages the rate may readily be increased to that of double thel normal rate.

Although I have herein shown and described only certain forms ofapparatus embodying my invention, it is understood .that various changes and modications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

l. A control system including a communicating circuit connecting two spaced locations, a generator of control current at each location,.means eiective at regular fixed intervals .to alternately supply current impulses from the generators to the communicating circuitand arranged in such a manner that an inactive period in which no current is supplied by either generator exists between said xed intervals, an electroresponsive means at each locationv biased to a receiving position for receiving current from the communicating circuit and selectively responsive tothe current from the generator atthe opposite loca.- tion, and an operating mechanism at each location governed by the electroresponsive means and maintained in an active condition by the impulses supplied at the regular fixed intervals. y

\ `2. A control system including, a communicating circuit connecting two spaced locations, coding means at one location adapted to establish an operating cycle of a given duration and to divide each cycle into several periods, a generator of carrier frequency current at each location, a plurality of generators of modulation current at each location, manually controlled means at said one location for modulating the carrier current by the diiierent modulation currents to establish diierent control currents, transmitting means governed by the coding means rendered effective during a given period ofeach operating cycle to supply an impulse of the established control current to the communicating circuit, a receiving means at the other location controlled by said circuit and selectively responsive to the different control currents, means governed by said receiving means to modulate the carrier current at said other location to form an indication current, a transmitting means at said other location effective during the period of the cycle immediately following an impulse of control current to supply to the `communicating circuit an impulse of the indication current, and a receiving means at said one location governed by said circuit and responsive to the indication current whereby impulses of control and indication currents are alternately exchanged between the two locations with at least one period of each cycle during which the generators a both locations are-inactive. Y v

1 3. A control systemincluding, -a communicating -circuit connecting two spaced locations, means at one location adapted to divide time into intervals of substantially equal lengths and to vsubdivide each interval into several equal periods, manually controlled means at `said one location for supplying different control currents to the communicating circuit and arranged to be active during but one period of each interval, receiving means at the other location adapted to receive the different control currents from said circuit for establishing different conditions of an operating mechanism, slow-release means normally effective to retain the operating mechanism in the established condition from the active period of one interval until the next, and means controlled by the receiving means for rendering the slow-release means ineiective upon a change in the control current.

4. The method of signaling between two spaced locations which consists in providing a generator of signaling current at each location, alternately transmitting impulses from each generator to the opposite location at recurrent intervals in such a manner that an inactive period in which no current is supplied by either generator exists between said recurrent intervals, and then providing an electroresponsive means at each location normally biased to a receiving position to receive the impulses transmitted from the other location and so arranged as to retain the effect of each received impulse until the next.

5. The method of signaling between two spaced locationswhich consists in providing a generator of current and an velectroresponsive means at each location with both electroresponsive means biased to a receiving condition, alternately transferring the two electroresponsive means to a transmitting condition, at .recurrent intervalsto supply impulses'from'each' generator to the other location in such a mannerthat an inactive period in which no current is supplied by either generator exists between said recurrent intervals, and then providing a signaling mechanism at each vlocationgoverned by its electroresponsive means in response to the received impulses and so arranged as to retain the effect of a received impulse until the next. f v L 6. The method or signaling between two spaced locations which consists in providing a generato-r of signalingcurrent at each location and a control means at one location which is adapted to divide time intov recurrent operating cycles with .each cycle subdivided into several substantially equal periods, causing the-generators to alternate-ly exchange impulses between the two locations once each cycle and arranged insuch a manner that during certain periods of each cycle no current is supplied by either generator, andy then providing an electroresponsive means at. each location to receive the impulse transmitted from the' other location and so arranged that each is set in a receiving condition except during the transmitting of an impulse from its locationv and each adapted to retain the effect of a received impulse until the next.

'7. The method of signaling between-two spaced locations which "consists in providing a generator of carrier current and a generator of modulation current at each location and a control means at one location having a recurrent operating cycle which is divided into several substantially equal perio'ds, causing the generatorsat each location to be active vduring one'period of eachcycle to transmitan impulse of modulated carrier current and so arranged that the generators at the opposite locations are -active during different periods' of the cycle with certain periods of each cycle in which no current is supplied by any of the generators, and'then providing an electroresponsive means at each location selectively responsive to the modulation of the carrier current of the opposite location andwhich are set in a receiving condition except as an impulse is transmitted from its location.

8. A control system for railway trains including, a source of control current and a source of signaling current at each of two spaced locations on a train, a brake control mechanism and a signaling device at each location, means for establishing a relatively slow code rate for alternately exchanging impulses of control current between the two locations for controlling each brake control mechanism by current irom the source at the other location, manually controlled means at each location adaptable when operated to cause the impulse transmitted from that location to be supplied by the source of signaling current to control the signaling device at the other location, and means eiective when either manually controlled means is operated to increase the exchange of impulses to a relatively high code rate.

9. A control system for railway trains including, a source of signaling current at each of two spaced locations on a train, a receiving means at each location adapted to be influenced by the current source at the other location, a transmitting means at each location, .a normally open signaling key at each location effective when closed to cause the transmitting means to periodically transmit code impulses of' current from the source at that location for inuencingthe receiving means at the other location, and a signaling device at each location governed both by the transmitting means and the receiving means whereby there is displayed at both locations a signal while either signalingkey is closed.

10. A control system for railway trains including, a source of current at each of two spaced locations on a train, a receiving means at each location adapted to be influenced by the current source at the other location, a transmitting means at each location, a normally open signaling key at each location effective when closed to cause the transmitting means to periodically transmit code impulses of current from the source at that location for influencing the receiving means at the other location, andI a signaling means at each location governed both by the transmitting means and the receiving means and operative to register the number of code impulses transmitted while either signaling key is closed.

11. A control system for railway trains including, a source of signaling current at each of two spaced locations on a train, a receiving means at each location adapted to be influenced by the current source at the other location, a transmitting means at each location, a normally open signaling key at each location effective when closed to cause the transmitting means to periodically transmit code impulses of current from the source at that location for influencing the receiving means at the other location, and a signaling means governed by each receiving means operative to register the number of code impulses received. f

12. Apparatus for the control of train brakes comprising in combination with the usual engineers brake valve on the locomotive, an auxiliary brake controlling mechanism located at another point on the train and capable of reproducing the different functions of the engineers brake valve and which mechanism includes a first electropneumatic valve capable of establishing a given brake application but normally biased to the inactive position and a second electropneumatic valve also capable of establishing said given brake application and normally biased to the active position, means for energizing the second electropneumatic valve in response to any one of the different control currents transmitted from the engineers brake valve for determining the position of the auxiliary brake mechanism, and other means responsive to a specific control current for energizing said rst electropneumatic valve.

13. Apparatus for the control of train brakes comprising in combination with the usual engineers brake valve on the locomotive, an auxiliary brake controlling mechanism at another point on the train capable of reproducing the different functions of the engineers brake valve, an electroresponsive means at each of the two points having a transmitting and a receiving position but both normally biased to the receiving position, control means to periodically transfer the electroresponsive means on the locomotive to its transmitting position for transmitting impulses of control current to the electroresponsive means at the other point to cause the auxiliary mechanism to register with the engineers brake valve, control means at said other point for transferring its electroresponsive means to the transmitting position for a period following the receipt of a control impulse to transmit impulses of an indication current to the electroresponsive means on the locomotive to establish an indication, and means to operate said two control means in such a manner that an interval in which no current is transmitted in either direction exists between an indication impulse and the next control impulse.

14. In combination, an electroresponsive means having a transmitting position and a receiving position and biased to its receiving position, an oscillating member having a predetermined frequency of oscillation, a first and a second relay, circuit means governed by said oscillating member for operating said relays and so arranged that the operating cycle for the relays covers two cycles of the oscillating member, means -jcintly controlled by said relays and said oscillating member for transferring the electroresponsive means to its transmitting position and so arranged that said means is effective only when said relays and said oscillating member have a predetermined relationship in their operating cycles.

ANDREW J. SORENSEN. 

